A steering wheel, a typical example of the resin-metal composite structures contemplated in the present invention, is generally produced by reactive injection molding (RIM) using a mold as shown in FIG. 1. A metal insert 1 is set on a lower mold 3, and the lower mold 3 is lifted and joined with an upper mold 5. A polyurethane material prepared by mixing a polyol component and an isocyanate component in a mixing head is injected into a cavity 7 formed in the closed mold to form a wheel main body 9 which is a resin molded part.
Adhesion between the wheel main body (resin molded part) 9 and the metal insert (metal part) 1 is usually secured by previously applying a rubber adhesive to the insert 1 to form an adhesive layer 2 as described in JP-B-7-53857.